\begin{tikzpicture}[scale=5]
    \coordinate(A) at (1,0);
    \coordinate(B) at (0,0);
    \coordinate(C) at (30:1);
    \draw (A) -- (B) -- (C);
    %\pic [draw=green!50!black, fill=green!20, angle radius=9mm,"$\alpha$"] {angle = A--B--C};
\end{tikzpicture}